The U.S. Environmental Protection Agency revised its proposed emissions standards for industrial boilers, saying the changes provided more flexibility.

The agency today issued the latest version of a plan to reduce emissions of air pollutants such as mercury and soot after announcing the rule Feb. 21.

While the agency is easing previous requirements to limit dioxin emissions from industrial boilers, it is adopting standards for mercury and hydrogen chloride that are “a little tighter than what we had proposed before,” Gina McCarthy, the EPA’s assistant administrator, said today on a conference call with reporters.

The rule, which may require upgrades of pollution controls at paper mills, chemical manufacturers and refineries, will cost $1.49 billion a year, about $90 million more than a previous estimate, because about 300 more boilers would be affected, the agency said in a fact sheet.